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#1
05-03-2018, 03:17 PM
 Deke Registered User FRC #0085 Team Role: Engineer Join Date: Dec 2013 Rookie Year: 2013 Location: Michigan Posts: 178
paper: FRC Pneumatic Cylinder Linear Speed

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FRC Pneumatic Cylinder Linear Speed by Deke
#2
05-03-2018, 03:24 PM
 Cyberphil That Guy FRC #0103 (Cybersonics), FRC 5666 (Purple Lightning) Team Role: Engineer Join Date: Feb 2008 Rookie Year: 2007 Location: Doylestown, PA Posts: 1,013
Re: paper: FRC Pneumatic Cylinder Linear Speed

Hey Deke (and other CD people),

I am working on a system that requires certain cycle times of pneumatic cylinders. This spreadsheet is very helpful but I am finding it a bit difficult to understand exactly what is going on having little to no formal training in real-life pneumatic systems myself.

My questions primarily deal with your first set of calculations, that being the effective area of the tube and solenoid. Do you have any literature I can find to help me understand these calculations and where you are pulling the constants and equations from?

Thank you very much.

-Phil
#3
06-11-2018, 10:52 AM
 Deke Registered User FRC #0085 Team Role: Engineer Join Date: Dec 2013 Rookie Year: 2013 Location: Michigan Posts: 178
Re: paper: FRC Pneumatic Cylinder Linear Speed

Hey Phil,

I missed the original post, but here is some information if you haven't found it already.

Here is a good site reviewing Cv and it's constants: http://kb.eng-software.com/display/E... e+Coefficient

Basically Cv = 27.66 * A * Cd

Since we are only told the Cv of the solenoid valves and not Cd, I set Cd to 1 and solve for area. This gets us close to where we need to be for the calculations.

For the tube effective areas, I simply calculated the area from the tube inner diameter and applied a .7 discharge coefficient (Cd). A .7 Cd is a fairly common starting point for discharge coefficients. Now this ignores the length of the tube, so you can adjust the Cd to account for that if needed.

Whenever we do hand calculations like this at my place of work, we do extensive testing to validate our calculations. Air flow and fluid flows are very sensitive to edge conditions (Cd) and need to be validated. We can get in the ball park, and the testing gets us zeroed in.

Hope that helps.

-Deke

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